I am working with Lamium amplexicaule plants under CuSO4 stress conditions. During my experiment an unidentified white substance have accumulated on the leaves of my plants. Looking at it through a binocular I saw that it wasn't fungai but rather some sort of substance that lies between the cells, and is accumulating near the main veins of the leaf so it's probably moving through the water system. I'm adding a picture of the plants with the mystery white thing on them. if anyone knows what it is or knows of a way to find out what it is i will be very grateful.